1. Field of the Invention
The present invention relates to a liquid crystal display device and a manufacturing method thereof, and a drive control method of a lighting unit, and in particular relates to a liquid crystal display device of a field sequential system and a manufacturing method thereof, and a drive control method of a lighting unit used for such a liquid crystal display device.
2. Description of the Related Art
As a color display system for a liquid crystal display device, the field sequential system is known in which the color display is performed by making plural different colors sequentially emit light at a predetermined period and performing an ON/OFF control of pixel electrodes in synchronization therewith, and is disclosed in Japanese Patent Laid-Open No. 2000-28984, for example.
The liquid crystal display device described in this publication includes, as shown in a perspective-projected view of FIG. 13, a liquid crystal display panel 50, a display drive control unit 57, a backlight 63 and a lighting drive control unit 64.
The liquid crystal display panel 50 is configured by laminating a polarizing film 51, a first glass substrate 52, a common electrode 53, pixel electrodes 54, a second glass substrate 55 and a polarizing film 56 in this order. Orientation films (not shown in the figure) are formed on facing surfaces of the common electrode 53 and the pixel electrodes 54, respectively, and a liquid crystal 65 is sandwiched between the orientation films. Corresponding to TFTs 58 which are switching elements formed at the intersections of plural gate lines 59 and plural source lines 60, plural pixel electrodes 54 are provided.
The display drive control unit 57 has a gate driver, source driver and so on, and is able to selectively supply a voltage signal to each gate line 59 and each source line 60 from the gate driver and the source driver. By supplying the voltage signal to the gate line 59, the TFT 58 connected with the gate line 59 can be switched, and a voltage is applied to the pixel electrode 54 from the source line 60 via the TFT 58 which is in ON state, thus capable of driving-the liquid crystal 65. Another configuration may be available in which the common electrode 53 is formed on the side of the first glass substrate 52, not on the side of the second glass substrate 55. Accordingly, a configuration similar to the liquid crystal display device of IPS (In-Plane-Switching) mode may be possible.
The backlight 63 has a light-guide/light-diffusing plate 631 and an LED array 632, and is located at a rear side of the polarizing film 56 (the lower side of the figure). In the LED array 632, as shown in a perspective-projected view of FIG. 14, light-emitting diodes (LEDs) which emit lights having respective R (red), G (green) and B (blue) colors are arranged in this order repeatedly on the surface facing the light-guide/light-diffusing plate 631, and the light emitted by each LED is diffused on the upper surface side of the light-guide/light-diffusing plate 631. The LEDs of respective RGB colors are controlled by the lighting drive control unit 64 to perform time-division light emission at a predetermined period. The light-guide/light-diffusing plate 631 can be divided into a light-guide plate and a light-diffusing plate.
The liquid crystal display device with the above configuration is capable of performing desired display by making each of the LEDs of the backlight 63 sequentially emit light by the lighting drive control unit 64, and in synchronization therewith, switching the TFTs 58 by the display drive control unit 57. An example of this operation will be described with reference to a timing chart shown in FIG. 15.
As shown in FIG. 15(a), a single field period is divided into three sub-field periods, and each TFT is switched to apply a voltage to each pixel electrode, thus driving the liquid crystal sandwiched between each pixel electrode and a counter electrode (hereinafter, to drive the liquid crystal in this way is referred to as “to write”). As shown in FIG. 15(b), after the writing in the first sub-field period is completed, the red LED emits light. Then, as shown in FIG. 15(c), the green LED emits light after the writing in the second sub-field period is completed, and as shown in FIG. 15(d), the blue LED emits light after the writing in the third sub-field period is completed. Thus, the light emission of RGB colors is repeated in each field period, which is the time-division light emission. Normally, the field period is 16.7 ms ( 1/60 sec).
According to the field sequential system like this, the effective transmittance of the backlight is improved in comparison with a conventional method employing a color filter, and the power consumption of the backlight can be reduced to ⅓ to ¼. However, since the light emission intensity is different among the LEDs of respective colors, it becomes necessary to modulate the chromaticity of display colors. In the above-described publication, a method of chromaticity modulation for display colors by making the light emission time for each color different is disclosed.
Conventionally, however, it has been difficult to obtain good white display because the method of modulating the light emission time of each color was not determined and only empirical rules or trial-and-error methods could be counted on. For example, since the light emission intensity of the red LED has been conventionally considered to be lower than those of the green LED and the blue LED, the above-mentioned publication shows that the white display is performed by making the light emission time of the red LED (8.33 ms) longer than those of the green and blue LEDs (4.17 ms). However, even if the LEDs of respective colors actually emit light for the above-described time, it is difficult to perform desirable chromaticity modulation, and there is still plenty of room for improvement in setting the light emission time of LEDs of respective colors.